Skip to content
Express Shipping

Express Delivery*

Free Delivery

30% OFF First Order*

Volume Discounts

Online Volume Discounts

Same Day Dispatch

Same Day Dispatch*

Express Shipping

Express Delivery*

Free Delivery

30% OFF First Order*

Same Day Dispatch

Same Day Dispatch*

Volume Discounts

Online Volume Discounts

Collection: Gusset Expansion Envelopes

When the contents are too thick for a standard envelope, a gusset expansion envelope provides the space without the need to move to a box. The expanding sides of a gusset envelope accommodate bulky documents, multi-page contracts, reports, catalogues, and legal bundles without straining the seams. Postal Packaging's range covers sizes from C6 through to C3, spanning 162x114mm up to 457x324mm, with peel and seal closure as standard on most lines. The gusset typically expands to 25mm, enough for a substantial document pack or several brochures. Available in white and manila finishes to suit both formal correspondence and practical dispatch.

6 products

Manila String & Washer Gusset Envelopes - No DL - 220 x 110 x 25mm

Manila String & Washer Gusset Envelopes

Regular price
Sale price From £0.71 Regular price £0.79
Black String and Washer Gusset Envelopes - DL - 220 x 110 x 25mm

Black String and Washer Gusset Envelopes

Regular price
Sale price From £0.76 Regular price £0.84
White String & Washer Gusset Envelopes - C4 - 324 x 229 x 25mm

White String & Washer Gusset Envelopes

Regular price
Sale price From £0.84 Regular price £0.93
Recycled Manila Gusset Peel & Seal Envelopes - 120gsm Without Window C6 - 162 x 114 x 25mm
Eco Product

Recycled Manila Gusset Peel & Seal Envelopes

Regular price From £0.25
Sale price Regular price
Red String & Washer Gusset Envelopes - DL - 220 x 110 x 25mm

Red String & Washer Gusset Envelopes

Regular price
Sale price From £0.76 Regular price £0.84
Recycled White Gusset Peel & Seal Envelopes - Without Window 254 x 178mm
Eco Product

Recycled White Gusset Peel & Seal Envelopes

Regular price From £0.23
Sale price Regular price

More About "Gusset Expansion Envelopes"

The Practical Solution for Thick Documents

A standard envelope is designed for a single sheet or a small number of pages. When contents exceed that, the envelope fails: the flap will not seal, the seams split, or the document folds under pressure. A gusset envelope solves this directly. The expanding base and sides create depth that a flat envelope cannot, and the peel and seal strip closes cleanly regardless of how much is inside.

When to Use a Gusset Envelope

  • Multi-page legal or financial documents that cannot be folded
  • Reports and proposals sent flat in C4 or C3 format
  • Catalogues, brochures, and promotional packs
  • Medical records or case files requiring a secure, flat envelope
  • Multiple documents dispatched together as a set

Size Guide

  • C6 (162x114mm): suitable for A6 documents folded twice, or small multi-page packs
  • DL (220x110mm): standard long document format with added depth for thick letters
  • C5 (229x162mm): A5 documents flat, or A4 folded once with several sheets
  • C4 (324x229mm): A4 flat, the most common size for reports and document packs
  • C3 (457x324mm): A3 flat, or large-format document bundles

Gusset Depth and Closure

Standard gusset depth is 25mm, which typically accommodates 20 to 40 sheets at 80gsm. Peel and seal closure is used on most lines for fast, secure sealing without moisture. String and washer gusset formats are also available for documents that require repeated access.

Trustpilot Verified

What Our Customers Say

See why we’re trusted as by thousands of UK businesses for packaging and envelopes through verified customer reviews.

Read more reviews at Trustpilot

Black and white photo of a person with long hair against a plain background

Aimée Thompson

We ordered some branded envelopes for a client event and they were a perfect addition. Jess and the team were extremely accommodating and attentive throughout the ordering process, pushing our order through to meet the tight deadline. I really recommend this company for branded materials. Thank you team!

Woman with long brown hair wearing a beige top against a plain background

Charlotte Goodman-Brooks

Great Customer Service

Unfortunately my order arrived damaged but after emailing the issue over to the company I received a quick response from Jess who was able to fix the problem in minutes, thanks so much jess, fantastic customer service, will definitely be ordering from this company again.

Man in a suit with a blurred green outdoor background

SR

Great Products, Quick Delivery

DPD were having issues delivering to my address and things were getting frustrating, but the company really stepped up. They sorted the problems with DPD quickly, the replacement arrived super fast, and they refunded my previous order without any hassle. Overall, I’m really impressed – amazing customer service, and I’ll definitely be ordering again!

Woman wearing a yellow sweater with a plain background

Grace

Proactive and Helpful

The courier let us down, but Jess and Kelly were hugely helpful and did everything they could to resolve it. They even arranged to specially stock products I order regularly to make future orders smoother. Great quality, good value and excellent customer service, with the phone answered on the first ring!

Woman with gray hair wearing a blue top against a light gray background

Rebecca R

Really Easy Process

Really easy process to order some custom printed envelopes, James was so helpful and answered all my questions. The envelopes arrived on time and are really great quality, wouldn't hesitate to use this company again!

Man wearing a light gray sweater over a collared shirt on a plain background

Bernie Webber

Great Company To Buy From

Great company to buy from. Very helpful and communicative.


Man wearing a dark suit with a red tie against a plain background

Paul Craig

Prompt and Efficient Service

Very helpful staff directing me to exactly the right item needed.

Man in a suit smiling outdoors with a blurred background

Richard

Fantastic Customer Service

Fantastic Customer Service